Cable ties and other forms of tie strip are widely used to quickly and easily secure items together. For example, sealing bags, bundling cables, or binding plants to stakes.
The conventional cable tie strip, as still widely used in industry, is first described by GB811973 (SOPACEM, Wrobel). It is generally injection moulded from nylon 66 and comprises a robust apertured head, extending from which is a slimmer flexible tail. In use, this tail portion is inserted through the remote aperture in the head, wherein a pawl engages with a series of ratchet teeth spaced along the tail. A constrictive loop is thus formed which can be tightened around the target.
modern examples of such cable ties are approximately 5 mm wide and 1 mm thick, with latching teeth spaced every 1.0 to 1.5 mm or so. The usual strength rating for such ties is 50 lbs (22.7 kg) when looped.
However, it has long been recognised that these ties are inherently inefficient, since after fitting, a significant portion of the tail is often wasted. To alleviate this, manufacturers are burdened with providing a wide variety of lengths, and users with stocking and selecting the most appropriate size for any given application. In practice, this seldom happens, and users frequently use oversized ties which inevitably leads to increased wastage.
In response, many inventors have tried to create more efficient “multiple-use” tie strips using various repeating sequences of interlocking apertures and latching members. Necessarily, the transverse width of the bulk strip is greater than the transverse width of the apertures through which it must pass, hence some deformation of the strip is required to allow threading.
Three general methods have been described in the known prior art, with the earliest ones being DE1079537 (Grzemba) and U.S. Pat. No. 3,224,054 (Lige). Both utilise longitudinal slots whose lengths are comparable to the greatest width of the strip. Consequently, a simple rotation of the free end by 90° allows the strip to readily pass through any chosen slot and form a loop. (A reverse 90° twist is then invoked to lock the tie in place.)
A second approach is to fold or curl the strip about its longitudinal axis, creating a more compact cross-sectional shape that better matches the width and shape of the provided apertures. This method is described in patents U.S. Pat. Nos. 3,913,178, 3,955,245, 3,973,610 and 4,077,562 (all Bailin), and also in U.S. Pat. No. 4,045,843 (Loose) and U.S. Pat. No. 4,150,463 (Brown).
The third method is to employ a chain of deformable cells that can laterally narrow and/or enlarge as the strip is pulled through itself. This may be done by use of mechanical spring portions that bend, or by using elastomeric materials that can stretch. Such approaches are described in U.S. Pat. No. 3,433,095 (Evans), U.S. Pat. No. 5,799,376 (Harsley) and U.S. Pat. No. 7,704,587 (Harsley).
Each approach has relative pros and cons, but a general consequence of all is a greater spacing between the latching points due to the introduction of the additional apertures. As a result, the latches typically end up 6 to 10 mm apart and the diameter of the tie can therefore only be adjusted in intervals of roughly 2 or 3 mm. This does not compare favourably with a conventional cable tie, which can be pulled much tighter with diameter adjustments below 0.5 mm.
The most effective solution so far has been the development of tie strips with the ability to stretch longitudinally, wherein applying additional tension draws the next latch through the aperture, allowing the tie to be pulled tight. This technique is described in the prior art of Evans and Harsley, and has led to commercially acceptable products. However, since these strips need to be stretchy to work, they are usually made from polyurethane rather than polyamide (nylon 66). Consequently they are not always a perfect replacement for convectional cable ties, being generally a little weaker and prone to sagging under heavy loads, especially in hot environments.
An alternative method is to retain a rigid strip, but implement sub-latches between the main latching points, as described by Loose and Brown. These are acknowledged as not being as strong as the main latches, but these ties are mostly intended for light duty applications such as hag tying where high strength requirements are not an issue.
U.S. Pat. No. 7,337,502 (Mermelshtein) takes this principle further by retaining the closely spaced latching teeth of the conventional cable tie design, but without the head portion. Instead, the apertures and latching pawls are formed by providing slits in the strip at required locations between the teeth. Deformation of the side walls during insertion then widens the aperture, allowing the strip to pass through itself. However, Mermelshtein states that his original design can only withstand up to 2 kg of force, and his improved ties little more than 8 kg. (WO2011039742, p 14.)
Looked at from a different perspective, the tie strips of Loose, Bailin and Brown may be compared to the ladder-style single-use tie strips described, for example, by U.S. Pat. No. 4,728,064 (Caveney) and U.S. Pat. No. 5,836,053 (Davignon). These follow the traditional cable tie design of apertured-head and extending tail, however the tail now comprises two parallel side rails extending between which are a plurality of rungs that co-operate with the head portion to function as latching members. The inventions of Loose, Ballin and Brown are essentially multiple-use variants of such ladder-style ties, and as noted in U.S. Pat. No. 4,473,524 (Paradis), their strength may be increased by cold-drawing to preferentially align the polymer molecules, albeit with an undesirable increase in rung spacing as well.
Ultimately, despite these numerous attempts, no waste-free alternative to the traditional Wrobel tie has yet been widely adopted by industry.